Protective coatings are commonly used to provide temporary protection for painted or polished manufactured articles against weathering, contamination from the atmosphere, chemical attack or accidental damage during handling and storage. Such coatings are applied to the painted or polished surface and are designed for facile removal without deleterious effect upon the surface to be protected.
Protective coatings are commonly used in the automobile industry to protect a newly completed vehicle from damage while being stored out of doors and during transport to the premises of a dealer. Waxes provide useful protective coatings when applied to a newly painted body creating a weatherproof, and to some extent, damage-resistant layer. However, such wax coatings can only be removed by employing an organic solvent, optionally in conjunction with a steam jet, thus involving flammability and/or toxicity hazards and the use of special equipment.
In order to overcome these disadvantages, alternative types of temporary protective coatings have been proposed which can be removed by treatment with solvents which are easier to handle and which do not adversely affect the environment. For example, U.S. Pat. No. 4,013,607 discloses an improved stable self-stripping aqueous coating composition containing as the primary coating agent an alkali soluble resin of low molecular weight and high acid number and aqueous ammonia sufficient to provide a pH of no less than about 9.0. The alkali soluble resin is an addition resin containing at least two ethylenically unsaturated monomers; one of the monomers being a ligand-free monomer such as vinyl acetate, styrene, ethyl acrylate and mixtures thereof, while the other ethylenically unsaturated monomer contains carboxyl functional groups including maleic, fumaric, itaconic and crotonic acids.
U.S. Pat. No. 4,540,736 discloses temporary coating compositions comprising water, a copolymer of ethylene and an .alpha.,.beta.-ethylenically unsaturated carboxylic acid having a number average molecular weight of from about 500 to about 5000 and an acid number of at least 100 milligrams of potassium hydroxide necessary to neutralize one gram of copolymer. The invention requires a sufficient amount of a base which is preferably volatile, to form a clear, aqueous liquid composition.
U.S. Pat. No. 4,562,226 discloses aqueous compositions suitable for forming upon a substrate a temporary protective coating which can be removed subsequently by treatment with an aqueous solution. The aqueous solution comprises a sterically stabilized aqueous dispersion of a polymer derived from monomers including at least one acrylic monomer and from 5% to 40%, based on the total weight of monomers, of an ethylenically unsaturated monocarboxylic acid, or an equivalent proportion of an unsaturated polycarboxylic acid.
U.S. Pat. No. 4,942,193 discloses a temporary protective coating for metals comprising a base-neutralized acid or base-functional copolymer which contains wax. Suitable acid-functional monomers are selected from acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and the like. Amounts of about 5 to 100 percent by weight of the acid-functional monomer based on the total monomer content can be employed. Typically, amounts of about 10 to 40 weight percent and preferably about 10 to 30 weight percent are employed. Copolymerizable ethylenically unsaturated monomers such as vinyl monomers, e.g., styrene, vinyl toluene and the like, esters of acrylic acid or methacrylic acid such as methyl methacrylates, butyl acrylate and 2-ethylhexyl acrylate, can be employed.
Manufacturers presently seek protective coatings exhibiting improved resistance to neutral aqueous solutions which can be removed at the desired time by treatment with aqueous alkali solutions.